Pressure switch assembly



March 13, 1956 E. M. TALBOT-r, JR 2,738,392

PRESSURE SWITCH ASSEMBLY Filed Deo. '7, 1951 2 Sheets-Sheet l if'r L 14 Q 1.,?" l l 15 M [/,1716 b a |l 1y@ 26 27 -Nl s lllllllIlIllll!llllllllll|\lllllll v BY my. @CE

ATTORNEY March 13, 1956 E.'M. TALBoTT, JR

PRESSURE SWITCH ASSEMBLY 2 Sheets-Sheet 2 Filed Dec. 7, 1951 ATTORNEY PRESSURE swrrcn ASSEMBLY Edwin M. Talbott, lr., Baltimore, Md., assigner to Bendix Aviation Corporation, Baltimore, Mtl., a corporation of Delaware Application December 7, 1951, Serial No. 260,364

3 Claims. (Cl. 200-83) The present invention relates generally to pressure responsive switch devices and more particularly to an improved pressure responsive switch especially adapted for use in connection with radiosonde apparatus.

Such switches are commonly designated as baroswitches and in general, comprise a supporting frame, an aneroid cell responsive to atmospheric pressure, an arm driven by the cell, so that one of its extremities traverses an arcuate path, and an electrical contact carried by the arm for cooperating with a switch block having a plurality of spaced conducting members thereon. When mounted in a radiosonde and sent aloft, up into the atmosphere, decreasing pressure will cause the pressure cell to expand and move the contact across the switch block.

Successive making and breaking of the contacts controls the action of reference and measuring circuits whereby audio-modulated radio frequency signals are generated by the radio transmitter. Each signal corresponds to a denite position of the contact and therefore can be translated in terms of atmospheric pressure.

Now the ordinary radiosonde is an expendable item in that the apparatus is tied to a balloon and sent aloft in a direction controlled by the winds prevailing at the time of night. Although each radiosonde is provided with a parachute to permit same to graduali return to earth after the point of maximum ascension has been reached (at which time the pressure differential across the balloon is suicient to cause the balloon to burst), actual practice in hundreds of thousands of flights shows a low recovery of the apparatus so returned to earth. Obviously, the radiosonde, meaning all of its components, must be constructed at the Ver;l lowest cost levels attainable, yet be of rugged construction to enhance the re-use of the equipment in those instances when same is recovered. This is also true of the military services where recovery of equipment is not of prime importance. Despite low recovcries, the units must be sufficiently rugged to permit reuse after ight without major salvage or repair attendant thereto.

Coupled with a continuous effort to reduce manufacturing costs, has been a continuous, ever-increasing demand for greater accuracy. For example, present requirements call for accuracies or" plus or minus 3 millibars in the very low pressure region as contrasted to plus or minus l millibars for baroswitches made ten years ago.

At the core of many of the problems surrounding manufacture of baroswitches is the problem of temperature compensation. The units must be able to work properly through a temperature range of plus 30 C. to minus 60 C. and this range in temperature, if not properly compensated for, would introduce errors of such magnitude that the baroswitch would be incapable of meeting the accuracy requirements.

Accordingly, the primary object of this invention is to provide a temperature-compensated baroswitch, com patible with minimum manufacturing costs and maximum accuracy, and sufficiently rugged to permit rough handling in the field and re-use after llights.

The objective is attained through a novel arrangement of parts and a careful selection of materials, and the advantages and novel features will be readily apparent upon purview of the detailed description set forth below, when read in conjunction with the drawings annexed hereto, in which:

Figure 1 is a plan View of the new and novel baroswitch;

Figure 2 is an end view of the baroswitch shown in Figure 1;

Figure 3 is a side-view of the baroswitch shown in Figures 1 and 2; and

Figure 4 is a partial View, in elevation, showing the shaft and associated parts for the lever arm actuated by the pressure cell.

Referring now to the drawings, the baroswitch has a frame 5 generally rectangular in shape, with one end slightly wider than the other, the frame being formed with an opening 6 in its narrow end. The frame 5 may be of aluminum and is stamped out by conventional sheet metal fabricating equipment. The edges of the frame 5, surrounding its periphery and surrounding the opening 6, are turned down to form anges 7, S respectively. The flanges add rigidity and ruggedness to the frame.

Located within the opening 6 and adjacent to the flanges S, is a pressure cell 9 in the form of co-acting diaphragms having driving and mounting studs 11, 12 respectively. The metal used for the diaphragme is a nickel-iron alloy, with small parts of titanium and chromium, known commercially as Ni-Span-C, and this material is characterized by a substantially zero temperature coeiiicient, i. e., the material is substantially unaffected by changes in ambient temperature.

A mounting support 13 for the pressure cell 9 is riveted to the frame 5 and it has a vertically extending boss 14 provided with a threaded aperture for cooperating with the threaded stud 12. A lock-nut 15 holds the cell 9 securely in place after it has been aiixed to the support 13. It is to be noted that the stud 12 encloscs the cell exhaust tubulation 16.

The driving stud 11 has a conical seat 17 cooperating with the pointed extremity of a pin link 1S. The other extremity of link 18 is pivotally secured to a ranging bracket 19 which in turn is carried by the U-shaped contact arm bracket 21. The bracket 21 has a shaft 22 extending through its side legs, the ends of the shaft being rotatably supported in the side legs of another U-shaped racket 23 riveted to the frame 5. Bracket 21 and shaft 22 are press-tit together to form an integral unit and bracket 21 is provided with an apertured ear 214i which holds one end of a spring 25, the other end of which is secured to a spring clip 26 frictionally engaging a reduced section ofthe driving stud 11. The upper leg of bracket 23 can be moved with respect to the lower leg by means of screw 20. This permits adjustment of the end-play in the shaft 22.

Considering this part of the mechanism so far described, any motion of the pressure cell will cause the bracket 21 to rotate about the axis of shaft 22 by virtue of the co-action between the driving stud 11, pin-link 18 and ranging bracket 19.

The ranging bracket 19 is adjustabiy mounted with respect to bracket 21 by means of screw 27 threadably engaging one end of bracket 19 through a horizontally elongated hole 28 provided in bracket 21. The other end of bracket 19 is slotted at 29 to cooperate with an inturned projection 31 kicked-up from bracket 21, and this arrangement preserves alignment of the brackets 19 and 21 when same are moved with respect to one another. An elongated slot 32 provided in bracket 19 is contiguous to aperture 33 in bracket 21 and this arrangement permits a simple tool (not shown) to be inserted into the cooperating parts (after screw 27 has been loosened) to shift them with respect to one another. From an inspection of the drawings, and upon consideration ofthe mode ot operation set forth above, any movement of the bracket 19 with respect to bracket 21 changes the leverage ratio of the driving linkage. This ratio must be adjusted from unit to unit to compensate for variations inthe pressure cells so that a predetermined motion range on the output end of the baroswitch is standard for each unit manu factured.

Afixed to the lower leg of bracket 21, by way of rivets or other suitable means, is an arm 34 carrying on its outer end the contact 35 and on its inner end the counterweight 3i). This arm may beof phosphor bronze or stainless steel and is given sutcient resiliency so that screw 36, cooperating with a threaded aperture in the offset extension 37 of the lower leg of bracket 21, can be adjusted to vary the contact pressure exerted by the contact 35. Counterweight 30 prevents whipping of arm 34- in case of severe vibration or shock.

Recapitulating, rotary movement of bracket 21 imparted by pressure cell 9 will cause the contact 35 to traverse an arcuate path, the exact length of which can be adjusted by means of shifting the position of ranging bracket 19, as aforesaid.

Cooperating with the contact 35 is a switch block` or commutator 38 mounted on the wide end of frame 5. The switch block 38 is a molded plastic member usually formed from polystyrene, and having an inlaid electrical contact pattern 39, the surface of the contacts and associated connectors, the surface of the block, and the surface of the portions of the block in between the contacts and connectors lying in one plane. The inlaid contact pattern 39 is only partially shown in the drawings and comprises an arcuate arrangement of a plurality of spaced conducting segments integrally molded into the plastic base member 38. Certain of the segments are interconnected through the pattern 39 so that repetitive switching is obtained as the contact 35 relays across the contact pattern 39. lt is to be noted that the Contact 35 has a very sharply defined contact point which contacts only one segment at a time as it moves across the Contact pattern 39. Each individual contact segment is separated by a segment of plastic insulating material. The plastic material selected for this unit possesses electrical insulating properties. In other words, the block presents a smooth polished surface at all points thereon, and the arrangement of the contacts, alternately spaced by portions of the block, suggests the common name by which these blocks are designated-namely, commutators.

Extending downwardly from beneath the commutator, and passing through opening 41 in frame 5, is a centrally located stud 42. The stud has an aperture intermediate its ends in one side of which is molded nut 43. Screw 44 passes through the stud 42 and cooperates with nut 43 to move the commutator as desired. Screw 44 also passes through the flanged edge of frame and has afxed to its outer end the detent knob or Wheel 45. Suitable Washers 46, 47 surround the screw, adjacent the stud 41 and the inner surface of the flanged edge of frame 5, respectively. Between the washers 46, 47 there is a coil spring i8 surrounding screw 44 to take up any play in the parts and maintain a steady positive driving force on the commutator. Cooperating with detent wheel 45 is the detent 49, suitably secured to the flanged edge of frame 5.

From the above arrangement, it is seen that the commutator can be moved along the axis of screw 44 simply by moving the detent wheel 45. This adjustment is necessary to Zero set" the commutator, i. e., shift the Contact pattern to line it up with contact 35 at atmospheric pressure.

The commutator 38 is held in place, and guided for motion by the leaf spring 51 pressing against its front edge to hold it against ythe guide members 52. Members 52 are part of frame 5 and are merely punched out and up to serve as guiding members. Also serving to hold the commutator in place is vthe retaining leaf spring 53. This spring surrounds stud d2 and has its outer extremities pressing against the under side of frame 5 and has its inner extremities pressing against nut 43 and washer 46.

Thus, the commutator is frictionally held in place by the leaf springs 51 and 53 and can be moved by rotation of the detent wheel 45. The use of stud 42 and-its location is a very important part of applicants invention and in a large measure completes the temperature compensation of the device. The plastic material ot the com- .iutator changes with temperature and by selecting the location o? stud 42, changes in dimension of the commutator can be controlled in such a way as to match the characteristics of `the pressure cell and connecting linkage, to thereby afford complete temperature compensation. Thus, in the extreme case, the stud could oe located at either end of the commutator, thus minimizing dimensionalchangcs at the end selected and permitting maximum changes at the free end. For the particular baroswitch shown, it was found that a central location was most effective, permitting both ends of the scale to change and minimizing changes in the central portion, thereby accomplisl'ting maximum compensation where most needed.

ln the arrangement shown, stud 42 is a separate part, molded o'l the same material as the commutator, and integrally joined by suitable connecting techniques. `The commutator and stud could be molded as one piece, if desired, without aitecting thc compensating action of. the arrangement.

Referring to the partial showing of the contact pattern 39, there are three circular areas, 5d, 55, 56. These areas connect to three groups of connected contact bars and are in turn connected by suitable leads 57, 58, 59, respectively, to appropriate terminals on the terminal board 61 affixed to the front edge of frame 5. Also connected to the terminal board by lead 62 is the contact 35 via the conducting arm 34 and jumper lead 63.

lt is desirable to elevate the Contact 35 slightly to prevent same from wiping over the contact pattern 39 during storage and shipment prior to actual useV of the device and to this end7 Contact lift bar 64 is provided,

suitably pivoted at 65, and having an actuating arm 66.

With the above arrangement of parts in mind, some of the important benefits und advantages accruing from the design are as follows: j

(l) An inexpensive but rugged frame is provided by a simple, formed sheet metal part. f

(2) A compact assembly is provided by the shape of the frame and the arrangement of parts thereon.

(3) Ranging of the unit is simpliiied by means of the action of the ranging bracket.

(4) Simple sheet metal parts are used throughout most of the assembly to provide for minimum manufacturing costs. f

(5) Complete temperature compensation is accomplished through the use of Ni-Span-C alloy material for the diaphra gms, proper selection of materials in the frame and connecting'linliage and the unique manner of mounting the commutators.

What is claimed and desired to be secured by United States Letters Patent is: y

l. A pressure responsive switch particularly adapted for a radiosonde, comprising, in combination: a generally rectangular flat supporting framehaving an opening formed through one extremity thereof, a pressure re sponsive element located in said opening and mounted on said frame, said element having a wall thereof adapted to move inl response to changes in ambient pressure, an

arm pivotally mounted at its one extremity on said frame adjacent said opening and having an electrical contact at its opposite extremity, a driving linkage connecting said contact arm to said movable `fvall, a ilat plate-like commutator coacting with said movable contact, said commutator being formed of electrical insulating material and having an inlaid contact pattern on its exposed outer surface over which said contact has movement and an internally-threaded stud projecting from its inner or opposite surface through an opening formed in the frame, said stud being located at a point intermediate the ends of the commutator, an adjusting screw having one extremity threaded through said stud and its opposite extremity accessible from the exterior of said frame for adjusting the commutator plate with respect to the frame, resilient means connected to said stud and frictionally engaging the adjacent frame Structure for holding the commutator in adjusted position, and means for guiding said commutator on said frame while at the same time holding it against lateral displacement, comprising a leaf spring anchored to the frame and engaging the adjacent edge of said commutator and one or more projections formed on said frame and engaging the opposite edge of said commutator.

2. A pressure responsive switch particularly adapted for a radiosonde, comprising, in combination: a generally rectangular at sheet-metal frame having an opening formed through one end thereof, a pressure cell located in said opening and mounted on said frame, said cell having a wall thereof movable in response to changes in ambient pressure, a switch arm, a substantially U- shaped bracket rigidly secured to one extremity of said arm and movable therewith, a driving linkage pivotally connected at one end to said bracket and at its opposite end engaging said movable wall, a substantially U-shaped supporting bracket connected to said frame, said irstnamed bracket and arm being located between the legs of said second-named bracket, a pivot pin projecting through the legs of said first-named bracket and journaled at its opposite ends in the legs of said second-named bracket, means for varying the spacing between the legs of said second-named bracket to thereby adjust the end play of said pin, said arm having an electrical contact at its opposite extremity, a flat plate-like commutator coacting with said movable contact, means movably supporting said commutator on said frame, said commutator having an inlaid contact pattern on its exposed outer surface over which said contact has movement and a supporting stud projecting from its opposite surface through an opening formed in the frame, and an adjusting screw coacting with said stud for adjusting the position of the commutator plate with respect to the frame. v

3. The combination defined by claim 2 wherein said driving linkage is in the form of a link pin having its one end pivotally engaged with said movable wall and its opposite end pivotally connected to a ranging bracket which in turn is adjustably connected to said first-named bracket.

References Cited in the tile of this patent UNlTED STATES PATENTS 238,094 dinfreville Feb. 22, 1881 1,140,433 Ames May 25, 1915 2,322,229 Diamond et al June 22, 1943 2,358,803 Hanson et al Sept. 26, 1944 2,367,034 McCabe Jan. 9, 1945 2,391,916 Newell Ian. 1, 1946 2,437,473 Ogden et al. Mar. 9, 1948 2,486,742 Gebhardt Nov. 1, 1949 

